feat(theme): R10 S1 — semantic status colors (danger/warn/success)

Add theme-scoped --danger/--warn/--success (+ -fg) tokens wired into the v4
@theme inline, replacing ~110 raw red/amber/emerald/green palette refs across
34 files. Fixes light-theme contrast failures (fixed Tailwind shades fell to
~1.7-3:1 on white). Status colors are scheme-independent — recognised by hue,
shifting only by theme to hold contrast (bright on dark bg, darkened on light).
Solid fills use the paired -fg text; @source inline guarantees the full -fg set
exists. IMDb rating gold kept as a deliberate decorative non-status exception.

frontend/src/components/Channels.tsx

@@ -1095,7 +1095,7 @@ function ActionsCell({
         <Tooltip hint={t("channels.row.unsubscribeHint")}>
           <button
             onClick={onUnsubscribe}
-            className="text-muted hover:text-red-400 shrink-0"
+            className="text-muted hover:text-danger shrink-0"
             aria-label={t("channels.row.unsubscribeOnYoutube")}
           >
             <UserMinus className="w-4 h-4" />